Tire having beads of specified structure

ABSTRACT

The invention relates to a novel tire having beads of a specified structure. In particular, the tire, when viewed in meridian section, has a radial carcass reinforcement and a bead of specified structure. The bead features a reinforcement ring that is able to move axially. The tire also features structures that are responsive to axial movement of the reinforcement ring, which modify clamping of the bead on its rim causing the clamping to increase with increasing tension of the carcass reinforcement.

This is a division of Ser. No. 09/239,168, filed Jan. 28, 1999, (nowU.S. Pat. No. 6,179,028) which was a continuation-in-part of Ser. No.08/682,548, filed Jul. 25, 1996 (now U.S. Pat. No. 5,971,047), which wasa national stage application of PCT/EP 95/00426 filed Feb. 7, 1995.

BACKGROUND OF THE INVENTION

The present invention relates to a tire intended to be mounted on a rimhaving at least a first frustoconical seat, the generatrix of which hasan axially outer end closer to the axis of rotation than the axiallyinner end.

Such a tire is described in international application WO 94/13498. Itcomprises at least a first bead, intended to be mounted on a first seatinclined towards the outside, the said first bead, having a seat thegeneratrix of which has its axially outer end closer to the axis ofrotation than its axially inner end, and the said generatrix beingextended axially towards to the outside by an outer face delimiting thebead toe, the said face forming with the axis of rotation an angle γ,open radially and axially towards the outside and of less than 90°. Theradial carcass reinforcement of the said tire, anchored in each bead toat least an inextensible annular bead ring, has a meridian profile, whenthe tire is mounted on its service rim and inflated to its servicepressure, with a constant direction of curvature in the sidewall andbead terminated by the toe and which is such that, in said bead, thetangent to the point of tangency of said profile with the inextensiblebead ring forms with the axis of rotation an angle ø open towards theoutside of at least 70°.

The bead of such a tire and more particularly the structure of theanchoring of carcass reinforcement may be variable. In the applicationWO 95/23073, the radial carcass reinforcement is anchored to theinextensible bead wire by winding around the said wire passing from theheel to the toe of the bead to form an upturn extending in a rubbersection, made of rubber mix in the form of a wedge defined by two sidescoming from an apex A located beneath the meridian section of the coatedbead wire, the radially outer side forming, with a line parallel to theaxis of rotation passing through said apex A, an acute angle ø₁, openradially towards the outside and between 20° and 70°, and the radiallyinner side forming with said parallel line an acute angle ø₂, openradially towards the inside, the rubber mix forming the rubber sectionaxially adjacent to the bead wire having a Shore A hardness greater thanthe Shore A hardness(es) of the rubber mixes located axially andradially above the wire and the rubber section.

The combination of the carcass reinforcement meridian profile such asdescribed in the first cited application with a structure of hookingsuch as described in the second cited application makes possible toobtain a very good compromise between the handling properties of thetire inflated to its recommended pressure and the said properties whenthe tire is inflated to a reduced pressure or even zero. Whether theinitial clamping on the rim be zero or of a given value, the axialdisplacement of the anchoring bead wire of the carcass reinforcement,which may result from the tension of said reinforcement, which tensionis due, for instance, to the inflation pressure of the tire, makespossible, in combination with the axial disposition of the rubbersection reinforced by the upturn, to obtain clamping of the toe of thebead on the rim seat. The value of this clamping increases as a functionof the tension force to which the carcass reinforcement is subjected,and may become great in the case of high tension, for instance when oneof the side walls of the tire is placed under great tension by atransverse force.

The preferential solution described in the application WO 95/23073 issuch that the carcass reinforcement upturn has a length such that it isin contact with the total perimeter of the rubber section or wedge; itthus forms the two radially outer and inner sides of the rubber sectionand the side opposite the apex or center of said rubber section, and itsend is located axially beyond the point of intersection of the two outerand inner sides. The part of the upturn immediately adjacent to the partof said upturn which is wound around the bead wire may, in the firstinstance, form the radially outer edge of the rubber section or wedgeand then finally the radially inner side of said rubber section, endingbeyond the junction point of the two outer and inner sides. It may alsoform firstly the radially inner side of the rubber section or wedge,then the side opposite the apex of said wedge, and then finally theradially outer side of said rubber section, ending in the same manner aspreviously described.

The above two structures are complicated and difficult to useindustrially, and as a consequence, expensive. Furthermore, in severeconditions of load, the contact pressure exerted by the bead toe uponthe axially outer hump of the rim and the great temperature that may bereached in the said bead are such that fissures of rubber may occur inthe external protecting layer of the bead, fissures which are propagatedalong the upturn of the carcass reinforcement and reach the radiallyinner face of the anchoring bead wire with destruction of the bead.

The invention has for object to remedy these drawbacks while keeping theexcellent properties of unseating of tire beads.

SUMMARY OF THE INVENTION

According to the invention, a tire with a radial carcass reinforcement,when viewed in meridian section, comprises at least a first bead, theseat of which has a generatrix the axially inner end of which is on acircle of a diameter greater than the diameter of a circle on which isthe axially outer end, the heel of the bead being axially on the insideand being reinforced by at least a reinforcement ring, annular,inextensible and coated with a rubber mix, the toe of bead being axiallyon the outside and comprising a rubber section made of rubber mix in theform of a wedge delimited by two sides coming from an apex A locatedbeneath the meridian section of the coated bead ring, the radially outerside forming, with a line parallel to the axis of rotation passingthrough said apex A, an acute angle ø₁, open radially and axiallytowards the outside, and the radially inner side forming with saidparallel line an acute angle ø₂, open radially towards the inside, therubber mix forming the rubber section axially adjacent to the bead ring,having a Shore A hardness greater than the Shore A hardness(es) of therubber mixes located axially and radially above the bead ring and abovethe rubber section, is characterized in that the carcass reinforcementof the said tire is wound, at least in the first bead, around the beadring passing from the inside to the outside to form an upturn extendingalong the radially inner side of the rubber section in form of a wedge,then along the side opposite the apex A, and then covers axially andradially on the outside, at least in part, the rubber section radiallyabove the rubber section or wedge, the said upturn having an end locatedradially above the reinforcement annular ring of bead and axiallybetween the straight line, extending the radially outer side of thewedge, and the straight line perpendicular to the axis of rotation andtangent at N to the said annular ring.

Preferably, the tire comprises a second bead, the seat of which has thesame configuration as the seat of the first bead, i.e a seat thegeneratrix of which has an axially inner end on a circle of diametergreater than the diameter of the circle on which is the axially outerend or seat inclined towards the outside.

The invention also provides a tire which, when viewed in meridiansection, has a radial carcass reinforcement and a bead of specifiedstructure. The bead comprises a reinforcement ring that is able to moveaxially. The tire further comprises means in each bead permittingmodification of clamping of the bead on a rim as a function of thetension of the carcass reinforcement. In one embodiment, the tirecomprises, viewed in meridian section, a radial carcass reinforcementand a bead having a reinforcement ring, the reinforcement ring beingable to be moved axially, and means responsive to the axial movement ofthe reinforcement ring for modifying clamping of the bead on its rim, sothat the clamping is increased with increasing tension of the carcassreinforcement.

If the diameter of a seat is the diameter of the circle on which is theend of its generatrix farthest from the axis of rotation, the tire haspreferably two seats inclined towards the outside and the two seats haveunequal diameters.

The meridian profile of the carcass reinforcement, when the tire ismounted on its service rim and inflated to its service pressure, has aconstant direction of curvature, at least in the first bead and thesidewall which extends it, and the tangent TT′ to the point of tangencyT of said profile with the reinforcement of the said bead forms with theaxis of rotation an angle ø open towards the outside at least equal to70°.

DESCRIPTION OF THE DRAWING

The invention will be better understood with reference to the drawingappended as FIG. 1 which illustrates a non-limiting example of anembodiment of a tire according to the invention, and which, whenassociated with a suitable rim, forms a high-performance tire-rimassembly. In this drawing, the figure shows a diagram of a tire beadaccording to the invention and mounted on the seat of its mounting rim.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The rim 2, on which the tire 1 is mounted, is formed mainly by twofrustoconical rim seats the generatrices of which form with the axis ofrotation an angle α′, open towards the outside of the tire, of between4° and 30°, and in the shown example equal to 14°, which is less thanthe angle of corresponding generatrices of the bead seats of the tire.The said seats have axially outer ends on circles, the diameters ofwhich are smaller than the diameters of the circles on which the axiallyinner ends are located. The seat 23″, mounted for instance towards theoutside of the vehicle, is axially extended on the outside by aprojection or hump 25″, the inner face 250″ of which forms with the axisof rotation an angle γ′, the diameter D_(SE) of which is less than theinner diameter D_(TE) of the bead wire 14 reinforcing the bead intendedto be mounted on the said seat, and the height h₁ of which, measuredwith respect to the axially outer of the rim seat 23″, is a heightcomparable with the height of humps or projections utilized axially onthe inside of conventional rims for passenger cars. On the outside ofthe vehicle, the rim seat 23″ is connected to a cylindrical bearingsurface 21 on which a bearing support will rest. The diameter of thecylindrical portion 21 is the nominal diameter of the rim.

The contour of the bead mounted on the seat 23″, comprises, axially onthe inside a wall 12D substantially perpendicular to the axis ofrotation and bearing laterally on the axially outer face of the bearingsupport. The said wall 12D is extended axially on the outside by afrustoconical generatrix 12C forming with the axis of rotation an angleβ of 45° which is open axially towards the inside and radially towardsthe outside. Said generatrix 12C is itself extended axially on theoutside by a second frustoconical generatrix 12B of the bead seat, whichforms with the direction of the axis of rotation an angle α′ of 15°,open axially towards the inside and radially towards the outside. Saidgeneratrix is said to be inclined towards the outside, its axially outerend being on a circle of diameter less than the diameter of the circleon which its axially inner end is located. A frustoconical generatrix12A, extending the generatrix 12B axially on the outside and forming anangle γ less than 90°, in the example equal to 45°, open axially andradially towards the outside, completes the contour of the base of thebead 12. The wall 12E, which is curved in the example described and isof substantially perpendicular general orientation to the direction ofthe axis of rotation of the rim, completes the contour of the bead.

Whereas the generatrix 12B will bear on the rim seat 23″, inclinedtowards the outside, the generatrix 12A will bear on the axially innerwall 250″ of the hump 25 of the rim 2, inclined by the angle γ′ equal tothe angle γ of the generatrix 12A. The portion of bead adjacent the wall12D and to the generatrix 12C forms, when viewed in meridian section,the heel of the bead. The portion of the bead adjacent the generatrix12B, the generatrix 12A, and partially the wall 12E forms the toe of thebead. The heel of bead is reinforced by the anchoring ring 14 of thecarcass reinforcement 13, the ring being coated with a rubber mix havinga high Shore A hardness. The toe of the bead comprises a rubber section3, arranged axially on the outside of the anchoring bead ring 14. Thisrubber section 3 is in the form of a substantially circular sector withan apex or center A located radially below the bead ring, with two sidesor radii 31 and 32 starting from said apex, and a third side 30 oppositethe apex A. The side or radius 31 radially on the outside forms an angleø₁ of 45° with a line parallel to the axis of rotation and it is openradially and axially towards to the outside, whereas the radially innerside or radius 32 forms an angle ø₂ of 15° with the same parallel lineand is open radially towards to the inside and axially towards theoutside. This rubber section is made of a rubber mix having a Shore Ahardness of 94 in the vulcanized state.

The coated bead ring 14 is surmounted radially on the outside by arubber section 7 of rubber mix having a Shore A hardness of 37. Radiallyon the outside of the rubber section 3 and axially on the outside ofsaid rubber section 7, there is located a third rubber section 6 made ofrubber mix having a Shore A hardness equal to that of the rubber section7 and therefor significantly less than the hardness of the mix of therubber section 3, which makes it possible, upon an increase of tensionof the carcass reinforcement, to facilitate the axial displacement ofthe ring 14 towards the outside of the bead and thus create acompression of the rubber section 3 and a self-clamping of the toe ofthe bead on the mounting rim 2, whereas, in the described example, theinitial clamping of the bead on said rim is practically zero, owing tothe quasi-equality between the angles of the rim and bead seats.

The carcass reinforcement 13 has a meridian profile, when the tire ismounted on its service rim 2 and inflated to its service pressure, whichhas a direction of curvature constant on its entire length, and is suchthat tangents TT′ to points of tangency T of said profile with thecoated bead rings form with the axis of rotation angles ø open radiallyand axially towards the outside and equal to 80°. The said carcassreinforcement 13 is wound around the coated bead ring passing from theheel to the toe of the bead, or from the inside to the outside, to forman upturn 130 extending along the radially inner side 32 of the rubbersection 3 in the form of a wedge, then along the side 30 opposite theapex A, and then covering axially and radially on the outside, at leastin part, the rubber section 6 radially above the rubber section or wedge3. The end of the said upturn is located radially above thereinforcement annular ring 14 of the bead and axially between twostraight lines, the line P₁ defining an extension of the radially outerside 31 of the wedge 3, and the straight line P₂ perpendicular to theaxis of rotation and tangent at the point N to the said annular ring 14.The so structured carcass reinforcement upturn 130 has a sufficientlength to have a good resistance to the unwinding of carcassreinforcement, while allowing a lesser propagation rate of fissuresoccurring in the external protecting layer 5 of bead, and to avoid thepropagation towards the annular bead ring 14.

We claim:
 1. A tire, viewed in meridian section, having a radial carcassreinforcement and a bead having a reinforcement ring, said ring beingable to be moved axially, and means responsive to said axial movement ofsaid ring for modifying clamping of said bead on its rim, so that saidclamping is increased with increasing tension of said carcassreinforcement.